1. Field of the Invention
The present invention relates to an ignition apparatus of an internal combustion engine wherein the generation of ignition sparks is prevented when the engine is reversely rotated.
2. Description of the Prior Art
FIG. 1 is a circuit diagram showing a conventional ignition apparatus of an internal combustion engine. In the diagram, a rotor 1 is driven by an engine (not shown) in the direction indicated by an arrow 2. The rotor 1 projects to a predetermined extent between positions A and B.
A sensor 3 is set to face the rotor 1 and detects first and second crank angle positions of the engine. The sensor 3 consists of a coil (winding), a magnet, and the like.
As shown in FIG. 2, when the front edge portion A of the projection faces the sensor 3, the sensor 3 outputs a positive voltage signal as a first angle signal. When the rear edge portion B of the projection passes in front of the sensor 3, the sensor 3 outputs a negative voltage signal as a second angle signal.
An anode of a diode 4 is connected to the output of the sensor 3 and a cathode is connected to a set input terminal S of a flip-flop circuit (hereinafter, referred to as FF) 6, respectively.
A cathode of a diode 5 is connected to the output of the sensor 3 and an anode is connected to a reset input terminal R of the FF 6, respectively.
Therefore, the sine wave of the output voltage of the sensor 3 passes through the diode 4 and is input to the set input terminal S of the FF 6, thereby setting the FF 6. The negative wave passes through the diode 5 and is input to the reset input terminal R of the FF 6, thereby resetting the FF 6.
A Q output of the FF 6 is input to a base terminal of a transistor 7 and a collector terminal is connected to a primary winding of an ignition coil 8.
The other end of the primary winding of the ignition coil 8 is connected to a (+) terminal of a battery 10 and a secondary winding is connected to the ground (the minus side potential of the battery 10) through a spark plug 9.
FIG. 3 shows an operation waveform diagram which assists in explaining the opertion of the circuit of FIG. 1. FIG. 3(a) shows a waveform of the output voltage of the sensor 3; FIG. 3(b) a waveform of the set input voltage of the FF 6; FIG. 3(c) a waveform of the reset input voltage of the FF 6; FIG. 3(d) a waveform of the Q output voltage of the FF 6; FIG. 3(e) a waveform of a collector voltage of the transistor 7; and FIG. 3(f) a waveform of a secondary output voltage of the ignition coil 8.
The operation will now be described. When the front edge portion A of the projection of the rotor 1 faces the sensor 3 due to the rotation in the direction of the arrow 2 of the rotor 1, the sensor 3 generates a positive voltage as shown in FIG. 3(a). A pulse such as that shown in FIG. 3(b) is input to the set input terminal S of the FF 6. Thus, the FF 6 is set and the output voltage at a Q output terminal of the FF 6 is set to high level as shown in FIG. 3(d).
Since the Q output of the FF 6 is at the high level, the transistor 7 is turned on (is made conductive) and a current flows through the primary winding of the ignition coil 8.
When the rotor 1 further rotates and the rear edge portion B of the projection passes in front of the sensor 3, the sensor 3 generates a negative voltage. Thus, a pulse as shown in FIG. 3(c) is input to the reset input terminal R of the FF 6 and the FF 6 is reset and the output voltage at the Q output terminal of the FF 6 is set to a low level.
Since the Q output of the FF 6 is at the low level, the transistor 7 is turned off (is made non-conductive) and the current to the primary winding of the ignition coil 8 is shut off. At this time, a high voltage as shown in FIG. 3(f) is generated on the secondary side of the ignition coil 8 and an ignition spark is obtained at the spark plug 9. In this manner, the above operations are periodically repeated in accordance with the rotation of the rotor 1 as shown in FIG. 3.
Since the conventional ignition apparatus of an internal combustion engine is constructed in the manner explained above, even though the operations described above involve no inconvenience, when the engine is started, the following drawbacks become apparent.
Assuming that the rotation of the rotor 1 in the direction of the arrow 2 is the forward rotation and the rotation in the direction opposite to the arrow 2 is the reverse rotation, when the rotor 1 is rotating forwardly, an output as shown in FIG. 4 is generated from the sensor 3 as explained above. In FIG. 4, t.sub.4 represents the output of the sensor 3 when the front edge portion A of the projection faces the sensor 3 and t.sub.5 indicates the output of the sensor 3 when the rear edge portion B faces the sensor 3.
On the other hand, when the rotor 1 is rotating reversely, the sensor 3 generates an output as shown in FIG. 5. The polarity (high or low level of the signal) of the output voltage of the sensor 3 which faces the crank angle position is opposite (in FIG. 5, t.sub.4a denotes the output signal of the sensor 3 when the rear edge portion B faces the sensor 3 and t.sub.5a indicates the output signal of the sensor 3 when the front edge portion A passes in front of the sensor 3).
Consideration will now be given to the case, where after the front edge portion A of the rotor 1 faces the sensor 3 in the forward rotation, the rotor 1 starts to reversely rotate before the rear edge portion B of the rotor 1 passes in front of the sensor 3, and the portion A passes in front of the sensor 3 during this reverse rotation. As shown in FIG. 6 [a in FIG. 6(a), d in FIG. 6(b), e in FIG. 6(c), and f in FIG. 6(d) are respectively the same as those in FIGS. 3(a), 3(d), 3(e), and 3(f)], the transistor 7 is turned on by the high level signal generated from the sensor 3 at time t.sub.1 as shown in FIG. 6(c). The transistor 7 is turned off by the low level signal generated from the sensor 3 at time t.sub.2 as shown in FIG. 6(c). As shown in FIG. 6(d), a secondary high voltage output of the ignition coil 8 is generated, and an ignition spark is thus generated by the spark plug 9.
The ignition spark generated at the front edge portion A of the rotor 1 further facilitates the reverse rotation of the rotor 1.
As mentioned above, there is a problem in that an ignition spark may be generated at the time of reverse rotation of the engine and the engine may consequently be damaged or the like.
FIG. 7 is a circuit diagram showing another conventional ignition apparatus for an internal combustion engine. In the diagram, sensor means SM detects the crank angle position of an engine (not shown). The sensor means SM generates an output signal which is changed from the high level to the low level at a first angle position .theta..sub.1 synchronously with the rotation of the engine and also generates an output signal which is changed from the low level to the high level at a second angle position .theta..sub.2 of the engine. This output signal is set to the low level (the first state) for the interval from the first angle position .theta..sub.1 to the second angle position .theta..sub.2 and is set to the high level (the second state) for the interval from the second angle position .theta..sub.2 to the first angle position .theta..sub.1.
The output of the sensor means SM is input to a base of a transistor 12. An emitter of the transistor 12 is connected to the ground [the (-) side potential of a battery 10]. A collector is connected to a (+) terminal of the battery 10 through a resistor 14.
A collector output of the transistor 12 is input to a base of a transistor 7. An emitter of the transistor 7 is connected to the ground. A collector is connected to the (+) terminal of the battery 10 through the primary winding of an ignition coil 8. A spark plug 9 is connected between a secondary output terminal of the ignition coil 8 and the ground.
FIG. 8 is an operation waveform diagram which will assist in explaining the operation of the apparatus shown in FIG. 7. FIG. 8(a) shows an output voltage of the sensor means SM. FIG. 8(b) shows a collector voltage of the transistor 12. FIG. 8(c) shows a collector voltage of the transistor 7. FIG. 8(d) shows a secondary output voltage of the ignition coil 8.
The operation of the prior art ignition apparatus shown in FIG. 7 will now be described. Since the first angle position .theta..sub.1 of the engine is detected at time point t.sub.1, the output signal of the sensor means SM is set to the low level and the transistor 12 is turned off. The transistor 7 is turned on (is made conductive) and a current therefore flows through the primary winding of the ignition coil 8.
Since the second angle position .theta..sub.2 of the engine is detected at time point t.sub.2, the output signal of the sensor means SM is set to the high level, the transistor 12 is turned on, and the transistor 7 is turned off (is made non-conductive). The following operation is similar to that of the prior art shown in FIG. 1.
However, assuming that the engine rotates in the reverse direction (the rotation in this case is referred to as reverse rotation) opposite to the present direction of rotation (the rotation in this case is referred to as forward rotation) of the engine at time t.sub.6 before the engine arrives at the second angle position .theta..sub.2, the engine passes through the first angle position .theta..sub.1 at time t.sub.7 in the reverse rotation state, so the output signal level of the sensor means SM is inverted from low level to high level (this operation is opposite to that which takes place in the case where, when the engine passes through the first angle position .theta..sub.1 at time t.sub.5 in the forward rotation state, the output signal level of the sensor means SM changes from high level to low level).
Since the output of the sensor means SM is set to the high level at time t.sub.7, the transistor 12 is turned on and the transistor 7 is turned off. Consequently, the current supply to the primary winding of the ignition coil 8 is shut off at time t.sub.7 and an ignition spark is generated by the spark plug 9, thereby further promoting the reverse rotation of the engine in the same way as in the prior art shown in FIG. 1.
Thus the prior art shown in FIG. 7 has the same problem as the prior art shown in FIG. 1, such as the risk of engine damage or the like.